Commitments and contingencies (Details)			6 Months Ended
	Jun. 02, 2015 USD ($) $ / shares	Dec. 10, 2013 $ / shares	Jun. 30, 2015 USD ($) ClinicalMilestone d Lawsuit	Dec. 31, 2014 USD ($)
Commitments and contingencies [Abstract]
Potential future payments			$ 7,500,000
Number of clinical milestones | ClinicalMilestone			2
Number of day's court afforded the plaintiffs to amend their complaint | d			30
Payments made on achievement of clinical milestones			$ 2,000,000
Potential future milestone payments on each additional final marketing approval			$ 1,000,000
Number of shareholders lawsuits | Lawsuit			3
Exercise price (in dollars per share) | $ / shares	$ 4.66	$ 2.39
Fees and expenses related to settlement	$ 1,100,000
Outstanding Receivable			$ 5,175,007	$ 2,019,293